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Lecture

Loudness Perception.docx

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Department
Psychology
Course
PSYCH 3A03
Professor
Paul Faure
Semester
Fall

Description
November 26 , 2013 Psych 3A03: Audition Loudness Perception Signal: Noise Determines Masking Threshold - Signal: Noise = E/N (0ower units) - S:N = E - N0(in dB) - Energy divided by the noise spectrum level - Where:  E = signal Energy  N0= noise spectrum level - For constant detection performance, the signal-to-noise ratio (i.e. energy of signal divided by noise power per unit of bandwidth) must be 5-15dB - The data also indicate that higher frequencies require larger S:N ratio in order to be detected The Critical Band – Our Internal Filter - Our ability to separate different frequencies depends on sharpness of our auditory filters - The data indicate that masking is most effective when masker frequencies are close to the probe frequencies - The physiology underlying auditory filters is already familiar to you - We wish to measure the bandwidth of the behavioural listening filters that we use for detecting signals - Assume listener detects probe signal by monitoring a critical band of frequencies centered on probe - Not measuring neuron filter; measuring integrative whole cognitive process - Measuring how wide is your listening filter - Vary the amplitude and bandwidth of the noise - Probe tone being asked to detect and assume that you have centered your listening filter on that one of interest - Narrowing the bandwidth of the noise until it starts to have an influence on your thresholds - Bandwidth of auditory internal filters t different frequencies can be measured psychoacoustically in masking experiments with humans - Diagram at right shows concept of critical band (triangle: critical band-pass filter; square: broadband noise) - When noise bandwidth completely fills the bandwidth of listening filter, maximum masking of signal occurs - When noise bandwidth narrows there is less energy falling inside critical band and thus it is easier (i.e. less masking) to detect signal in noise Signal:Noise Ratio Within Critical Band - When noise bandwidth completely fills the bandwidth of listening filter, maximum masking - When noise bandwidth narrows there is less energy falling inside critical band and thus it is easier (i.e. less masking) to detect signal The Critical Band: An Analogy - Providing a tone that is being filtered by the basilar membrane based on the tone - Tone can be moved which moves the filter - When the noise is narrowed: that is the noise band that masks detection - Decreasing signal to noise ratio makes detection easier Fletcher’s Band Narrowing Experiment - Fletcher performed band-narrowing experiment to measure the width of critical (internal)
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